Interop 2026: The State of Web Platform Compatibility
The web platform is fragmenting—or is it? Interop 2026 marks a significant milestone: the overall cross-browser compatibility score has reached 95, up from 25 just a year ago. Here’s what this means for web developers.
The Core Insight
Interop is a cross-browser initiative bringing together Apple, Google, Igalia, Microsoft, and Mozilla to solve the most frustrating browser compatibility issues. The 2026 cycle tackles 20 focus areas and 4 investigation areas, covering everything from brand-new CSS features to edge cases in existing APIs.
The headline number is impressive: overall interop score jumped from 25 to 95. But as Mozilla’s article notes, the real win isn’t passing tests—it’s ensuring features work consistently across browsers in the real world.
Why This Matters
For web developers, browser inconsistencies have historically meant wasted hours debugging why something works in Chrome but breaks in Safari. Interop targets these pain points directly, focusing on features that:
- Are well-defined in stable web standards
- Have good test suite coverage
- Matter to developers (via surveys and bug reports)
The 2025 cycle delivered cross-browser support for features like CSS Anchor Positioning, the Navigation API, and View Transitions. These aren’t just specs—they’re features developers actually wanted.
Key Takeaways
New Features in Interop 2026:
– Cross-document View Transitions: Animate between pages without JavaScript
– Scroll-driven animations: Drive animations based on scroll position (replacing heavy main-thread solutions)
– WebTransport: Low-level HTTP/3 API for multiple unidirectional streams
– CSS container style queries: Apply styles based on container computed values
– Scoped Custom Element Registries: Different shadow roots can define different elements with the same tag name
– CSS shape(): A CSS-native syntax for clip-paths and offset-paths
Focus Areas (carried over from 2025):
– CSS Flexbox, Grid, and scroll snap edge cases
– Navigation API reliability
– WebRTC improvements
– JavaScript top-level await
Investigation Areas:
– Accessibility tree consistency across browsers
– Mobile viewport testing
– JPEG XL support
– WebVTT (video captions)
Looking Ahead
Mozilla notes something important: achieving good test scores doesn’t always mean consistent behavior. Some focus areas in Interop 2025 required going back to fix specs and tests that contradicted intended behavior.
The lesson: test coverage isn’t enough. Browser vendors need to collaborate not just on implementations, but on the specifications themselves. With Interop 2026, that collaboration is stronger than ever.
Based on analysis of Mozilla Hacks “Launching Interop 2026”